In the past decade, with the rapid development of three-dimensional modeling technology, a lot of three-dimensional scenes such as Google Earth quickly appear, however, the navigation technology based on a three-dimensional scene has not been well developed.
Currently, there have been many technical researches on the camera control and the three-dimensional virtual scene navigation, mainly concerning the automatic and semi-automatic technologies about viewpoint selection, camera trajectory selection and camera movement control.
The researches on viewpoint selection such as viewpoint entropy. Utilizing entropy to measure the distribution of the building facades under the specific view. Analyzing the viewpoint significance using descriptors including building surface visibility, object significance, curvature, profile and topology complexity; and analyzing the semantic features of some definitions (including style, position, structure, etc. of the building) based on intelligent learning.
The researches on camera trajectory planning, for example, using the path planning and the graph searching technology to navigate automatically in a three-dimensional museum; and technologies such as collision detection, object visibility analysis and path smoothing from the perspective of geometrical analysis. The above methods mainly consider the generation of the camera trajectory while omitting the camera moving speed. Later, some researches proposed an optimization method of automatically calculating a camera moving speed based on a predefined camera path, which mainly considers keeping the user's attentions.
The researches on camera movement such as movement mode between interest value points predefined by the user. The above method adds a manner of accepting the user's feedback and simple interaction during the navigation.
The automatic navigation methods based on a three-dimensional scene at present mainly have the following problems: firstly, many navigation technologies are still based on fixed camera speed, viewpoint and height, without considering scene features and the user's attention; secondly, many navigation technologies are not fully automatic, and most of them require the user to make a number of calibrations and inputs; thirdly, the existing navigation technologies are very limited during usage, and can only be applied to a special scene; and fourth, the visual perception during the navigation is not so continuous or smooth enough.